<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div>
    <button onclick="fn()" ondblclick="fn1()">点击</button>
    </div>
</body>
<script>
    let timer =null
    function fn() {
       clearTimeout(timer)
       timer =setTimeout(function(){
        alert('2班')
        console.log("2班")
       },500)
        // btn.removeEventListener('click',fn);
    }
    function fn1() {
        clearTimeout(timer)
        alert('4班')
        console.log("4班");
        
    }

</script>
</html>